Trevor Siemian, the third-year pro and former seventh-round pick, was going to be the starting quarterback for the Broncos in 2017. That much Vance Joseph believed he’d be able to count on in his first season as the team’s head coach.

“It’s a huge deal to name a starter at any position,” Joseph said Aug. 21. “It’s a permanent decision. Obviously, outside of injury, that’s different. But as far as Trevor being our guy, he’s our guy.”

Fast forward three months and the Broncos are making their third change at the quarterback position in 12 games, marking one of the most turbulent, unstable seasons at the position in franchise history. It’s the first time the Broncos have started more than two quarterbacks in a season since 2003, when Jake Plummer, Steve Beuerlein, Danny Kanell and Jarious Jackson made up a starting list of four quarterbacks for the first time in the team’s NFL history.

Were Chad Kelly, the Broncos’ seventh-round pick back in April, not on the injured reserve and ineligible to play, the Broncos may be tempted to match the record in a season that has only further complicated a quarterback puzzle with pieces that have been scattered since Peyton Manning retired after lifting the Super Bowl 50 trophy.

Before 2003, you have to go back to John Elway‘s rookie season in 1983 to find the last time the Broncos used three starting quarterbacks. And this is just the seventh time since the AFL-NFL merger in 1970 that the Broncos have started more than two quarterbacks in the same season. The common thread in all of those seasons: None included a playoff victory.

“That’s not good,” Joseph said. “When you’re playing with three quarterbacks — not because of injury — it’s not a good thing. We have to find the right guy for our football team, and that’s where it starts in this league. All three guys have worked hard. Again, when you don’t have success at the quarterback level, it’s a lot of things. It’s blocking and it’s throwing and catching. It’s all those things. It’s details. I can’t say it’s all of those kids’ fault. It’s a unit issue. But it starts with the quarterback.”

Siemian was benched after Denver’s seventh game, a 29-19 loss at Kansas City in which he threw three interceptions, continuing a string of turnover-prone play. Enter Brock Osweiler, who went 0-3 in three starts and threw fewer touchdowns (three) than interceptions (four). Then, in Joseph’s words, it was former first-round draft pick Paxton Lynch‘s turn. But that turn, on Sunday at Oakland, lasted just three quarters before Lynch suffered a high-ankle sprain that could keep him out as long as four weeks.

So now it’s back to Siemian, who will start against the Dolphins at Miami on Sunday and give interim offensive coordinator Bill Musgrave his second quarterback in two weeks in his new role. And it’s another change for an offense that hasn’t produced consistent rhythm since its Week 2 victory over the Dallas Cowboys. For an offensive line that has struggled with its own rotating door at right tackle and a rookie at left tackle, and a receiving corps hampered at times by injuries and inconsistency, juggling quarterbacks has only added to the problems in a disastrous 3-8 season.

And all of the change at quarterback in the last two seasons follows a stretch in which Manning started 57 of Denver’s 64 games in the regular season from 2012-15.

“We have played with three this year, and it has been ups and downs with all,” Broncos wide receiver Demaryius Thomas said of the quarterback turnover. “So we just go out and do our job as receivers and go out and run our routes and try to get open. The ball comes our way, we just make the play.”

Joseph had reason to believe, after a 2-0 start that featured some of the best play of Siemian’s brief career, that he wouldn’t be consumed in the weeks to come by a mess at the game’s most important position. Yet, in recent weeks, he hasn’t been able to name a quarterback for anything longer than a one-game stretch. And that’s no different after the third change in five weeks.

Revolving doorA look at the seasons in Broncos history, since the AFL-NFL merger in 1970, with the most turnover among starting quarterbacks. Games a quarterback started in a given season are in parentheses:

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